Raised patio question

[DIYHacker]

Hi all

 

Looking for a bit of advise on a current project I am doing at home.. When moving in there was a deck out the back that was rotting so I finally decided it was time to replace it before one of us feel through the boards. I didn't want to go through having a deck again and want something more permanent so decided on a raised patio as the land is lower than the bifold door level. I mapped out the area and got a digger/operator in to dig the trench. I decided on using concrete blocks for the retaining wall and because of the lay of the land I need to use a 2 block high wall so the trench had to go down further to accommodate the 2 brick high wall. 

 

When chatting with the digger guy, he said I should go about 30cm below my line for the base so that was done.. Now I am looking to fill that space and thought that I had to use concrete but when doing searching a came across a few other posts that said you could just use MOT and compact it down.. 

 

So my question is, is that an option? To lay 30cm of compacted MOT down, then a bit of mortar and lay the bricks or does it need to rather be a concrete base? The other thing is when reaching out to a couple concrete supply places, you only get 45min - 1hr offload time and when trying to offload 2.2m3 with one wheelbarrow that won't be enough time and to rent a concrete pump will cost a lot more than what the concrete is on its own.. Whereas I can get the MOT in one loose delivery and can move it at my own pace..

 

 

[ProDave]

Are you suggesting to lay MOT in the trench, then pour concrete then build the wall?  That is not normal.  Normal is concrete in the trench blocks straight onto that.

 

It would be cheaper to buy a few more wheelbarrows and get some mates or paid labourers to barrow it round.  Preparation of the rout is important to avoid steps or other obstructions.

[Conor]

Haha. No. Chance. Get a couple mates and extra wheel barrows. Or hire a compact dumper. It'll cost you about £300 more than compacted stone, but it wont fall over in a couple of years.

 

I helped a mate out last year, 4 guys, 5m³concrete in less an hour through a house and into the garden.

[saveasteading]

In a foundation use solid concrete. Under a slab or patio use type 1 first.

Do you have an onsite mixing supplier nearby. Technically 'volumetric'.

They will do it a barrow at a time, but you still need to shift it fast. Or they can sometimes bring a pump with them.

Phone your suppliers and explain that it will take 2 hours and see what they suggest.

 

OR mix it on site, a barrow at a time, and you have control and a sore back.

[DevilDamo]

Make sure you’re aware of the Planning implications as anything over 300mm requires approval… even if it is a replacement. 

[Conor]

Oh, one more thing, make sure to don't cause damp issues by building above your DPC or blocking weep holes.... Need to be properly detailed e.g. linear drains etc.

[scottishjohn]

may not be applicable 

i was in same postion at back door 

so I built a wall then put block and beam on top and finished off with paveeing blocks  never gets wet 

i did drill a few small  drainage holes in retaining wall so water did not gather up below 

that was 20 years ago and still fine 

 a quick shot out of the window 

[DIYHacker]

Ok great.. So looks like best practise will be the concrete.. Unfortunately no chance of extra labour/hands so would just be me so probably best to buy the materials loose and slowly mix onsite by myself as the extra cost for the pump really pushes costs up..

 

Attached a pic of the area.. New patio won't be more than about 20cm above ground due to the fall of the one corner..

 

 

 

 

[DIYHacker]

Hi all

 

So there has been a development.. Yesterday there was a burst mains mater pipe further up the road and this is what I woke up to this morning..

 

Basically, we live rural and there is a drainage ditch along the road at the top of the property. What we never knew was that it seems this drains through our property into the pond that you can see in the one picture. That pond then has a drain pipe that goes under where the patio is going to be (I have covered it with the paving stones in the pictures to protect from the concrete pour) and out the other side in to another ditch which flows down through my neighbours property and out in to another rural ditch..

 

Over the past couple of years this pond has over flowed to the extent where our garden looks like a swimming pool and we thought it was ground water running off from the neighbouring field but after yesterday's incident, I now think that the majority of the water is running in from further up the road and can't filter out fast enough from our pond..

 

But that is something else we now need to figure out..

 

My question is, if I put down 300mm of concrete in the ditch, when we next have heavy rain and the water comes up from the water table from the pond, will that damage the concrete/patio in some way?! Or is 300mm enough to keep it down?!

 

 

[saveasteading]

7 minutes ago, DIYHacker said:

I put down 300mm of concrete in the ditch, 

Then you are blocking the ditch. A bad thing.

Am I misunderstanding?

[DIYHacker]

@saveasteading Sorry, not ditch, I meant trench.. U-shape in front of house where foundation for raised patio is going to go

[Conor]

1. Concrete will be fine with high water table.

2. You'll need to have proper protection for the drain pipe. A paving flag wont be enough. Something like a a 100mm concrete head cut in to lengths.

3. You'll need to scrape out the bottom of those tranches and compact before pouring concrete.

4. Get your digger driver back for a half a day to do the above and they can use a large bucket and track the concrete from the lorry and place in to the trenches. 

5. Finally, you'll need to scrape out all that soft crap in the middle after the trench pour. you'll then put down enough compacted stone to bring it up to the required level for paving.

[DIYHacker]

@Conor

 

Ok thanks, that's a relief on point one!

 

With regards to the protection around the pipe, I used a few of the concrete blocks for the sides with the flag stone on top. The pour of the concrete will be level with that flag stone. Will that still be ok?

 

Digger driver doesn't do half day unfortunately.. I will let that all dry out and hit it with the wacker plate before pouring the concrete..

 

The soil in the middle will be scraped off to help fill out the trenches once the concrete is down and the 2 high concrete bricks are laid.. Then as you say, will fill up with hardcore to bring it all level..

[ProDave]

11 minutes ago, DIYHacker said:

The soil in the middle will be scraped off to help fill out the trenches once the concrete is down and the 2 high concrete bricks are laid.. Then as you say, will fill up with hardcore to bring it all level..

Only use that soil to fill in around the outside of the trenches.  Do NOT use it to fill in the inside of the trenches which will eventually support your patio, it WILL settle, you will not be able to compact it enough.

 

The idea digging foundation trenches is you scrape them flat as you go with the digger bucket, you don't leave loose stuff in the bottom and if you do you remove it, not compact it down.  You are trying to pour on stable undisturbed ground, not partly infilled stuff on top of it.

[scottishjohn]

you need some access to the drainge pipe for when it gets blocked  so concreting in where it seems to change direction is not good -

myabe you should not be building over it ?

[DIYHacker]

On 12/09/2024 at 10:13, ProDave said:

Only use that soil to fill in around the outside of the trenches.  Do NOT use it to fill in the inside of the trenches which will eventually support your patio, it WILL settle, you will not be able to compact it enough.

 

The idea digging foundation trenches is you scrape them flat as you go with the digger bucket, you don't leave loose stuff in the bottom and if you do you remove it, not compact it down.  You are trying to pour on stable undisturbed ground, not partly infilled stuff on top of it.

Cool, thanks for the info. If you shouldn't backfill inside with soil, should i just fill that with more MOT and compact that down?

 

[DIYHacker]

17 hours ago, scottishjohn said:

you need some access to the drainge pipe for when it gets blocked  so concreting in where it seems to change direction is not good -

myabe you should not be building over it ?

There is no change of direction, its just one long pipe.. I am putting a grill over both ends so to ensure that its only water that passes through when needed so should be fine.